Telescopium, Microscopium and neighboring constellations, as depicted in 18th-century Urania's Mirror.

Nicholas-Louis de Lacaille invented over a dozen constellations to fill gaps in the southern sky map. Instead of looking to classical mythology, he celebrated the instruments of the Enlightenment. Two small faint constellations represent extremes of visual aids – the telescope and the microscope.

Telescopium – now diminished
Lacaille's original Telescopium was bigger than the one we know now. Stretching up between Sagittarius and Scorpius, it represented an aerial telescope of the kind Jean-Dominique Cassini used at the Paris Observatory. Rather than having a tube, an aerial telescope was suspended from a tall structure.

In order to make the constellation, Lacaille incorporated some stars from other constellations. But later astronomers returned them to their original constellations. For example, Lacaille's star Beta Telescopii represented the pulley at the top of the mast shown in Lacaille's drawing.

The stars
Telescopium
The brightest star of Telescopium is Alpha Telescopii, which had formerly been part of Corona Australis. It has a visual magnitude of 3.5. That's a measure of how bright it looks to us on Earth, not its absolute magnitude, which is a measures of its intrinsic brightness. The bigger its number on the magnitude scale, the dimmer a star appears.

The limit of unaided human vision is magnitude 6. The magnitude of very bright stars is a negative number. The brightest star in our sky is Sirius at magnitude -1.5. Yet Alpha Telescopii is actually far brighter than Sirius. Although Sirius is 25 times brighter than the Sun, Alpha Telescopii is 800 times brighter. However Alpha Telescopii is about 30 times farther away from us than Sirius.

In fact, although Telescopium is dim to us, even in ideal viewing conditions, almost all of its stars that are visible to the unaided eye have negative absolute magnitudes.

Telescopium [as of September 2019] has no stars with confirmed planets. Yet some are known to have brown dwarf companions. A brown dwarf is a failed star. It began nuclear fusion, but wasn't massive enough to sustain it. There are also a few stars with debris disks. Eta Telescopii has both a brown dwarf and a debris disk. Such a disk provides the material to make planets.

Microscopium
Dimmer even than Telescopium, without optical aids you could only see Microscopium in a clear dark sky.

Its brightest star, Gamma Microscopii, is the eyepiece of the microscope. It's a yellow giant about 2.5 times the mass of the Sun. Today it's some 225 light years away, appearing to us as a fifth magnitude star. Yet four million years ago it was only a few light years away. If our distant ancestors had gazed at the sky, the star would have looked brighter than Sirius does today. It may even have come close enough to disturb comets in the distant Oort Cloud that surrounds the Solar System.

You'd need a telescope to see the star BO Microscopii. It has a nickname – Speedy Mic – from its fast rotation. About the size of the Sun, it's somewhat less massive. The Sun takes almost 25 days for one rotation, but Speedy Mic does it once every nine hours. It's also very active compared to our more sedate Sun, and not only releases more radiation, but most of it is high-energy radiation.

We know of two star systems – WASP-7 and HD 205739 – that have a Jupiter-sized planet. The former has a hot Jupiter, a giant planet in a close orbit to its star. HD 205739's planet's orbital period is 280 days, which is similar to that of Venus around the Sun.

Two other stars – young red dwarf star AU Microscopii and sunlike HD 202628 – have debris disks. Eta Telescopii's brown dwarf may have disrupted the formation of planets there, but they could still form around the two Microscopium stars. There is evidence suggesting HD 202628 has a planet.

Deep-sky objects
These two small constellations aren't known for their deep sky objects. British astronomer Patrick Moore even described Microscopium as “totally unremarkable”. That was a bit unfair. It may not offer much to amateur astronomers, but it has its points of interest.

The Telescopium Group is a cluster of about a dozen galaxies some 120 million light years away. NGC 6861 is one of the brightest galaxies in the cluster. It's an example of a lenticular galaxy, neither spiral nor elliptical, but with features of each. The dark bands are dust lanes which are typical of spiral galaxies. The white oval shape shows an enormous number of stars in the center of the galaxy. Such a compact oval is typical of an elliptical galaxy. [Image: NASA/ESA Hubble Space Telescope]

In 1834 British astronomer John Herschel discovered NGC 6845 in Microscopium in 1834. He had no idea what it was, but we now know that it's a quartet of galaxies. Two of them are spiral galaxies that are interacting strongly with each other. A supernova was observed in one of them in 2008. A supernova is the enormous explosion that results from the collapse of a massive star when it runs out of fuel.

Microscopium contains the Microscopium Supercluster and the Microscopium Void. A supercluster is a cluster of galaxy clusters. But the void is just as interesting. It's an enormous area of space without any galaxies and a generally low density of matter. It's a puzzle for cosmologists.